Feet-Inch Fraction Calculator
Add and subtract measurements the way they read on a tape measure: 12' 6 3/8", 6-3/8 or 3.2m. See the answer in feet, inches and fractions, decimals and metric.
How this feet-inch calculator works
Everything is converted to inches, calculated in decimal, then converted back. That avoids the mistakes people make carrying fractions by hand. The ft-in answer is rounded to the nearest 1/2, 1/4, 1/8, 1/16 or 1/32 inch (your choice); the decimal and metric lines are not rounded. A measurement with no unit is treated as inches, and 25.4 mm equals one inch exactly.
Diagonal tool
The diagonal is the Pythagorean theorem: the square root of width squared plus length squared. To square a foundation, deck or wall layout, measure corner to corner both ways. If the two diagonals match, the corners are square. The 3-4-5 triangle is the same math with whole numbers.
Equal spacing tool
With n balusters of width w between two posts a distance L apart, there are n + 1 equal gaps. Each gap is (L − n × w) ÷ (n + 1), and the center-to-center spacing is that gap plus w. The model residential code (IRC R312.1.3) says guard openings must not allow a 4-inch sphere to pass, so we flag any gap of 4 inches or more. Your local code and the plans for your project come first, and stair guards have additional opening rules.
A planning aid, not a substitute for measuring twice. Check critical dimensions on site.
Sources
Estimates only — not engineering, legal or code advice. Check requirements with your local building department and a licensed professional before you build.
Common questions
How do I add feet and inches with fractions?
Type each measurement and join them with +. For example 12' 6 3/8" + 3' 4 1/2" gives 15' 10 7/8". The calculator adds the fractions, carries 12 inches into a foot for you and shows the answer rounded to the precision you pick (1/2 to 1/32 inch).
What formats can I type?
Feet and inches (12' 6 3/8" or 12'-6 3/8"), inches only (6-3/8, 6 3/8" or 150.5"), decimal feet (12.5'), and metric (3.2m, 3200mm, 320cm). A number with no unit is read as inches, the way a tape measure works. Put spaces around the minus sign when subtracting, such as 10' - 3 1/2", so it is not mistaken for the dash in 6-3/8.
How do I multiply or divide a measurement?
Use x or × to multiply and ÷ to divide by a plain number. For example 8' 4" ÷ 5 = 1' 8" and 2' 3 1/4" x 4 = 9' 1". Dividing one length by another gives a plain ratio.
What does the precision setting do?
It sets the smallest fraction the ft-in answer is rounded to: 1/2, 1/4, 1/8, 1/16 or 1/32 inch. The decimal and metric lines are not rounded. For example 3.2 m is 125.984 in, which reads as 10' 6" at 1/16 inch.
How do I check that a layout is square?
Measure both diagonals of the rectangle. If they are equal, the corners are square. Use the diagonal tool for the number you should see: a 12' x 16' rectangle should measure 20' 0" corner to corner. The 3-4-5 rule is the same idea, since 3' and 4' sides give a 5' diagonal.
How many balusters do I need on a railing?
Guards generally must not let a 4-inch sphere pass through (IRC R312.1.3), so the clear gap between balusters must be under 4 inches. For an 8' (96 in) run with 1 1/2 in square balusters you need at least 17, which leaves gaps of about 3 15/16 in. With 16 the gaps would be 4 1/4 in. Always confirm the rule with your local building department.